Gearbox cover



FIG. 1 is a front perspective view of a gearbox cover;

FIG. 2 is a rear view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines shown represent the portions of the gearbox cover that form no part of the claimed design. 

CLAIM The ornamental design for a gearbox cover, as shown and described. 